Some types of dump trucks that travel in mines are known as the series hybrid type. Such series hybrid type dump trucks generate electric power with a generator driven by the engine and supply the electric power to rear wheel motors for driving the rear wheels. By taking advantage of the electrical configuration of the series hybrid type, traveling technology based on the trolley system has been implemented. In the trolley-based traveling technology, trolley wires generally employed for electric trains are installed in prescribed climbing sections. In the climbing sections with trolley wires, a vehicle having power collectors (provided on the vehicle to be movable up and down) travels not by using the electric power supplied by the engine and the generator but by using electric power acquired from the trolley wires by elevating sliders of the power collectors to be in contact with the trolley wires (hereinafter referred to as “trolley traveling”). An example of the trolley-based traveling technology has been described in Patent Literature 1, for example. In this case, the drop in the traveling speed in the climbing sections (equipped with the trolley wires enabling the trolley traveling) can be avoided since the electric power supplied from the trolley wires is greater than the electric power generated with the engine power.